1. Field of the Invention
This invention relates generally to touchpads. More specifically, the invention relates to clear touchpads that can be disposed over a viewing or display screen such as on a computer monitor, a PDA or a mobile telephone, wherein the touchpad is capable of determining which zone a user is touching on the display screen.
2. Description of Related Art
The state of the art of touchpads has become more varied as new applications and devices have been created to use them. A touchpad is fundamentally a touch-sensitive device, generally found to be operating using the principles of resistance sensing, capacitance sensing, optical sensing or other means of sensing touch.
As experimentation with touchpads has increased, it was determined that touchpads can be disposed over a clear substrate, where the electrodes that define the sensory boundaries of the touchpad are made from clear or nearly clear inks, such as indium tin oxide (ITO). The electrodes can also be made from very thin wires, although this method introduces some difficulties. Thus with a relatively see-through or clear touchpad, it can be disposed over a display screen and operated much like a touchscreen as known in the prior art.
The substrate upon which the electrodes of the clear touchpad are disposed can be rigid or flexible, but as a practical matter, the substrate should be relatively thin. A thin substrate simply helps to make the clear touchpad as transparent as possible. Transparency is important because of the nature of the display screen that is likely to be underneath the clear touchpad. In other words, the display screen may not be a particularly bright screen. Thus, in order to help the user by not increasing eye strain, the display screen should be dimmed as little as possible from passing through the substrate and electrodes of the clear touchpad.
Good materials for substrates that are relatively clear and through which a user can see a display screen include KAPTON®, MYLAR™, KADADEX®, polyethylene napthalate (PEN®) and other materials having similar mechanical and electrical properties.
The focus of this document is directed towards a clear touchpad. The preferred embodiment is thus for a clear touchpad that provides limited touchpad functionality, defined herein as zone detection. However, clear touchpads are not limited to single layer touchpads. Therefore, this document also addresses a touchpad having complete touchpad functionality by using two layers of touchpad electrodes.
Complete touchpad functionality is generally characterized as providing cursor control for a computer, television, or a portable electronic appliance such as a PDA, camera, mobile telephone, etc. Accordingly, such a touchpad requires at least two layers of sensing electrodes when the touchpad uses capacitance sensing technology, such as that provided by CIRQUE CORPORATION. Multiple substrate layers and thus multiple or overlapping layers of electrodes generally results in a touchpad that is mostly transparent, but can be difficult to see through. This becomes a problem of usability when the touchpad is disposed on the display screen.
It is worth noting that attempts have been made to make the substrate layers and the inks used for electrical traces to be thinner and therefore to have greater apparent transparency. The attempts so far have still resulted in a display screen that is uncomfortably dimmed by the touchpad electrodes.
Accordingly, what is needed is a touchpad providing complete touchpad functionality that is more transparent than those in the state of the art in order to provide greater viewing comfort to the user.